1. Field of the Invention
This invention relates to improvements in sealing devices for the rim space between the inner wall of a storage tank and the periphery of a floating cover therein.
2. Description of the Prior Art
Bulk fluids such as petroleum and fuel products are usually stored in large cylindrical tanks. These are commonly designed with floating covers to minimize product losses to the atmosphere. A critical part of the floating cover is the sealing mechanism that is installed in the annular space (rim space) between the floating cover and the inner wall of the storage tank. This sealing mechanism is designed to allow the floating roof to float on the stored product, to maintain a vapor seal, to move easily within the tank as the product levels rise and fall, and to keep the floating cover centered within the tank.
The sealing ring, or shoe type seal, has proven over the years to be the most effective type of sealing device. The shoe type seal consists of a sealing ring that completely encircles the inner periphery of the storage tank wall. This sealing ring is formed of segments that overlap. This configuration allows for expansion and contraction of the sealing ring segment joints. The most common methods of expansion joints are (1) the use of flexible fabric at every 3-5 shoe segments that is riveted or bolted to the shoe segment, and (2) the use of a metal expansion joint that is formed into the shoe segment. The metal expansion joints allow expansion and contraction that allow gaps or openings that exceed accepted gap criteria and promote product loss and environmental pollution.